Chapter 13. Exceptions

Table of Contents

Errors

Try..Except

Handling Exceptions

Raising Exceptions

How To Raise Exceptions

Try..Finally

Using Finally

Summary

Exceptions occur when certain exceptional situations occur in your program. For example, what if you are going to read a file and the file does not exist? Or what if you accidentally deleted it when the program was running? Such situations are handled using exceptions.

What if your program had some invalid statements? This is handled by Python which raises its hands and tells you there is an error.

Errors

Consider a simple print statement. What if we misspelt print as Print? Note the capitalization. In this case, Python raises a syntax error.

		
>>> Print 'Hello World'
    File "<stdin>", line 1
      Print 'Hello World'
                        ^
SyntaxError: invalid syntax

>>> print 'Hello World'
Hello World

Observe that a SyntaxError is raised and also the location where the error was detected is printed. This is what an error handler for this error does.


Summary		Try..Except